Traits for solvers (optimization and Krylov)

[abelsiqueira]

This involves SolverCore, all solvers, and JSOSuite, possibly changing the definition of JSO-compliant (ref. #38), and also @dpo and I had a discussion some time ago about this, in the context of allowing specific Krylov solvers for the subsolvers (JuliaSmoothOptimizers/JSOSolvers.jl#85).

Instead of creating a table to inform what the solvers are capable of, we could use traits.
This allows dispatching, which should also help make things type-stable.

A normal implementation of traits is what is called Holy traits:

abstract type TraitHandleBounds end
struct CanHandleBounds <: TraitHandleBounds end
struct CannotHandleBounds <: TraitHandleBounds end

HandleBounds(::Type) = CannotHandleBounds()
HandleBounds(::Type{TrunkSolver}) = CanHandleBounds()
some_bounds_foo(solver::T) where {T} = some_bounds_foo(HandleBounds(T), x)
some_bounds_foo(::CannotHandleBounds, x) = x
some_bounds_foo(::CanHandleBounds, x) = -x

Do we want this? Is there a better alternative?